Question about sours, and lactic acid concentration

[bracconiere]

So i've got a sour beer, not on purpose. but it tastes allright/good? so i'm drinking it.

Problem, is i added my glucoamylase as always. but got a FG of 1.006 instead of my usual 1.000.

now lactic acid has 3.6 calories a gram. i tried to google a lactic acid solution with a SG of 1.006, to try and figure out how many grams of lactic acid are in my beer. no luck.

Any smart people here that can help me out with this? yes this is assuming that the beer fermented 'dry', just the lactic acid jacked up the FG reading...

 

[ajdelange]

You won't be able to determine anything from SG. If you want to know how much lactic acid is present you determine that by titration.

 

[bracconiere]

damn good idea, thanks...so pull 'x' amount of beer...add baking soda till it stops bubbling and do mol math on the result....

get me close enough i think, i know that it's not the only acid present though. but something to look into....

edit: so i weighed 157g's beer....it took 5 g's of baking soda to neutralize it....mol of baking soda is 84... atomic weight of sodium is 22, looks like lactic would accept one sodium atom....


22/84=.26*5....i get 1.3 g's of 'acid', or a ~1% solution....so in a 340g beer, i'd have like an extra 10 cal's and not worth noting...

problem solved

 

[Silver_Is_Money]

For what it's worth, roughly 5 grams of baking soda will neutralize 5 mL of 88% Lactic Acid.

 

[ajdelange]

I've never thought of using "when it stops bubbling" as an end point indicator but crude as it is I suppose it's sufficient for the purpose at hand (and pretty clever too). I'm not sure what the concern is here but it seems it may be the contribution of lactic acid to the caloric content of the beer.(?) As lactic acid is a fermentation end product in humans I expect that it contributes 0 calories when consumed.

 

[bracconiere]

I've never thought of using "when it stops bubbling" as an end point indicator but crude as it is I suppose it's sufficient for the purpose at hand (and pretty clever too). I'm not sure what the concern is here but it seems it may be the contribution of lactic acid to the caloric content of the beer.(?) As lactic acid is a fermentation end product in humans I expect that it contributes 0 calories when consumed.

lol, 'evolution of co2 ended' sound fancier?

And, yes, according to wikipedia lactic acid has 364/100g's (or something like that) calories...not sure if it's like gasoline/motor oil and not use able...but wanted to see how many grams were in a glass for calorie counting reasons...only way i can stay thin

But the baking soda test is good enough to tell me i'm only dealing with a couple grams a glass so, not to worry about it..now to buy some lactic acid, add a couple grams to plain water, and confirm it's not carbs and actually lactic acid raising the SG!

Thanks again for the pointer, after you said that, i was googling about similar and it pointed me to a thread here from 2010 where you said about the same thing to someone else asking a similar question!

edit: anyone here willing to sacrifice 2g's of lactic acid and save me having to buy a bottle?

 

[Silver_Is_Money]

Roughly 9-1/2 grams of pure lactic acid per bottle does not seem to be trivial. How did you get into this mess? It almost seems as if a full pint of 88% lactic acid was added to a roughly 5.5 gallon batch of beer.

 

[bracconiere]

Roughly 9-1/2 grams of pure lactic acid per bottle does not seem to be trivial. How did you get into this mess? It almost seems as if a full pint of 88% lactic acid was added to a roughly 5.5 gallon batch of beer.

It was an infected batch...But i'm thinking it actually has about 2.6g's lactic per 12oz glass? which would be a 1% solution....or .8, whatever...anyway, i can't seem to get google to tell me what a 1% lactic solution's SG would be, it does tell me white vinegar or 5% acetic is 1.006 though, and lactic is denser then acetic....

Nothing too serious, just dorkin around...

edit: your right, to use the atomic weight of sodium to figure moles of lactic i'd have to weigh how much the beer gained wouldn't i....anyway i'm sure there's other acids involved, i did test it with a ph meter at end, it went from 3.8, to 6.7...anyway i'm confident, it's not loaded with calories now...

 

[RPh_Guy]

88% lactic acid is 1.209

 

[bracconiere]

what about 1%?

 

[RPh_Guy]

If it's linear, then 1.002

 

[Silver_Is_Money]

I get closer to 1.0007 as the SG for 1% lactic acid by weight in distilled water, but it simply doesn't work this way at all. There are too many other things in the beer besides lactic acid and water.

If 157 grams of this beer required 5 grams of baking soda for neutralization, then the equivalent of ~5 mL of 88% lactic acid was present within the 157 gram sample. Each 12 ounce bottle would thereby have closer to 11.25 mL equivalent of 88% lactic acid in it. And that is close to 9.65 grams of pure lactic acid powder in every bottle. Call it ~2.7% lactic acid beer.

 

[ajdelange]

Remember, and I think someone else mentioned this, that lactic acid in a sour beer isn't the only source of buffering to be considered. Fizzing is such an crude end point indicator that one really can't draw much of definitive worth from it. Even were a proper titration done with a pH meter one would have no way of knowing how much of the buffering came from the beer itself and how much from the lactic acid. One could, suppose, measure he buffering of a similar non spoiled beer and deduct that from the total assuming the difference to be attributable to lactic acid.

 

[Silver_Is_Money]

A.J., this matter of lactic acid got me thinking about the relationship between lactic acid as a percent by weight concentration vs. pH for the case of lactic acid in distilled or DI water. I whipped up a quick spreadsheet to solve for this and it gave the following output, which does not seem at all right, as at first glance a 10 fold increase in acid should presumably drop pH by 1 full point, but going from 1% lactic acid by weight to 10% lactic acid by weight is not dropping the pH by anywhere near 1 full point. Am I on track or way off base here? I can email you a copy of the spreadsheet for your review if you like.

The output of my spreadsheet:
1% lactic acid in distilled water: pH = 2.407
5% lactic acid in distilled water: pH = 2.056
10% lactic acid in distilled water: pH = 1.903
50% lactic acid in distilled water: pH = 1.535
88% lactic acid in distilled water: pH = 1.394

 

[ajdelange]

as at first glance a 10 fold increase in acid should presumably drop pH by 1 full point, but going from 1% lactic acid by weight to 10% lactic acid by weight is not dropping the pH by anywhere near 1 full point. Am I on track or way off base here?

Not way off base but off base a bit. When the solution is very dilute a tenfold increase in the lactic acid concentration will drop the pH by about one. For example, 1 mL of 88% lactic acid in 10,000 litres of water would give a pH of 5.93 and 10 would give 4.96. 100, however, drops it it 4.12 and 1000 to 3.46. This is because when you mix the acid (HLac) with the base (H2O) protons are transferred from the acid to the water such that the protons lost by the acid (which is not all of them) is equal to the number taken up by the water. In order to do the calculation one, as is the case in any acid/base problem, tries various pH's and computes the net charge on the lactate and the net charge on the water. The pH which results in those being equal and opposite (sum = 0) is the pH.

 

[Silver_Is_Money]

When I use the same spreadsheet that I referenced above for Phosphoric acid it indicates that 10% by weight phosphoric acid in DI water should have a pH of 1.06. This is for: molecular weight = 97.995, mMoles/mL = 1.07396 (for 10%), pKa = 2.15 and Ka = 7.0795 E-3 (whereby 10^-pKa = Ka)

Does this pH result sound even remotely ballpark correct?

 

[ajdelange]

The first step is to calculate the mass of 1L of a 10% w/w solution of phosphoric and divide that by 10. That's thethe of phosphoric acid in the liter. Now divide that by the molecular weight to get the moles of phosphoric acid that corresponds to. Now guess an initial pH. 1 isn't a bad stating pH. Compute the charge 1 mole of phosphoric acid at the trial pH. It is probably OK to ignore the second and third pK's of phosphoric acid as long as your pH trials are less than say 5 but if you are going to be doing this sort of thing to any appreciable extent it's going to be handy to have a function which computes the charge on a mole of an arbitrary acid as a function of all of its pK's. Once you get Q/mol or mmol multiply by the number if mols (or mmol) of H3PO4.

Next determine the volume of the water in the liter of solution and compute the charges on it as mol*(10^-pH - 10^(pH-14)) . Add the phosphoric acid charge (negative) to the water charge (positive). If the sum is bigger than 0 increase the pH repeat the calculation. If the sum is less than 0 try a lower pH and repeat. This is a great place for Newton's method or root bisection.